An improved air-gap flux control method of a bearingless induction motor based on the optimized mutual inductance

To address the magnetic saturation in bearingless induction motors (BIM)-which limits suspension force enhancement under increasing suspension current-an improved air-gap flux control method is proposed. This method reduces the air-gap flux to a minimal operational level, thereby improving motor efficiency. Firstly, the magnetic saturation problem is revealed by the finite element analysis (FEA) and the impact of the suspension system is presented. Afterwards, combined with the BIM's equivalent circuit, the relation between the stator current, the exciting current and the rotor current of the rotation module and the suspension module is discussed. On this basis, the minor air-gap that can satisfy the normal operation is determined and the improved air-gap flux control is proposed. In addition, the accuracy of the decoupling system is enhanced by investigating the mutual inductance of the BIM. The numerical analysis and simulation results prove that the proposed methods can successfully restrict the impact of the magnetic saturation problem and strengthen the operation performance of the BIM.